The ultrasonic emission efficiency of ultrasonic transducer can be improved by superposition of the ultrasonic waves emitted from an ultrasonic transducer and the reflected ultrasonic waves. In its designs of reflecting ultrasonic confocal microscope, Japanese patent No. JP6102260 adopts this method to increase acoustic fields at the sample to be observed so as to improve the imaging quality of ultrasonic microscope.
German patent No.: DE3131796 (Title of the invention: Scanning ultrasonic microscope) adopts two confocal spherical shell ultrasonic transducers, which have a common focal point. One transducer acts as ultrasound source for transmitting ultrasonic waves and the other acts as a receiver for receiving ultrasonic waves which obtains the image of the substance from the received signals.
However, the two patents as mentioned above only disclosed that using two ultrasonic transducers or one of them replaced by a reflector so as to increase the acoustic field at the focal point of microscope, but the ultrasonic emission efficiency of ultrasonic transducer hasn't been improved in a vast scale.